. Bulletin. Agriculture -- New Hampshire. TILE DRAINAGE 25 and, second, the average distance oi the ground water below the surface. Commonly speaking, four feet is con- sidered deep drainage, three feet medium and two to two and one half feet shallow. In heavy, retentive clay soils it is advisable to lay the tiles between medium and shallow for two reasons: First, because the water filters through them so slowly that it takes a long time to reach the drains, and, second, because the cost of digging increases very rapidly with the depth in a hard clay soil. In a more porous, loamy soil experien
. Bulletin. Agriculture -- New Hampshire. TILE DRAINAGE 25 and, second, the average distance oi the ground water below the surface. Commonly speaking, four feet is con- sidered deep drainage, three feet medium and two to two and one half feet shallow. In heavy, retentive clay soils it is advisable to lay the tiles between medium and shallow for two reasons: First, because the water filters through them so slowly that it takes a long time to reach the drains, and, second, because the cost of digging increases very rapidly with the depth in a hard clay soil. In a more porous, loamy soil experience has shown that the most practical depth is about three feet. The second condition mentioned above, which affects the depth, is important in this respect, in that the level of the ground water changes with the season and is usually highest in the spring. If the ground water then comes too near the surface only in the spring and naturally lowers itself later on in the season it may be desirable to lay the drains only deep enough to dry the land for plowing and cultivation at the proper time. Shallow drainage will usually suffice where this condition of affairs is to be met. On the other hand, when the ground water is not sufficiently low at any season of the year for the maximum development of the roots, it is best to resort to deep drainage, and unless the soil is a retentive clay the tiles may be placed from three and one half to four feet Fig. 1. Showing effect of soil and depth of drains on distance apart. Line XY indicates surface of ground. Line ABCDE indicates surface of ground water in porous soil with tile 2 feet deep and 50 feet apart. Line FHS indi- cates the same for tile 3 feet deep and 100 feet apart, the ground water hav- ing the same slope and coming equally near the surface in both cases. Line AMCPE indicates surface of ground water in retentive clay soil with tile 2 feet deep and 50 feet apart, while line FNS indicates the same for tile 3 feet deep and
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